This application relates to integration of optical fibers on substrates to form various optical devices, and more specifically, to techniques and designs for integrating optical fibers in grooves formed in substrates.
Optical fibers are widely used in transmission and delivery of optical signals from one location to another in a variety of optical systems, including but not limited to fiber links and fiber networks for data communications and telecommunications. A typical fiber may be simplified as a fiber core and a cladding layer surrounding the fiber core. The refractive index of the fiber core is higher than that of the fiber cladding to confine the light. Light rays that are coupled into the fiber core within a maximum angle with respect to the axis of the fiber core are totally reflected at the interface of the fiber core and the cladding. This total internal reflection provides a mechanism to spatially confine the optical energy of the light rays in one or more selected fiber modes to guide the optical energy along the fiber core.
The guided optical energy in the fiber, however, is not completely confined within the fiber core. A portion of the optical energy xe2x80x9cleaksxe2x80x9d through the interface between the fiber core and the cladding via an evanescent field that essentially decays as an exponential function of the distance from the core-cladding interface. The distance for a decay in the electric field of the guided light by a factor of e≈2.718 is about one wavelength of the guided optical energy. This evanescent leakage may be used to couple optical energy into or out of the fiber core, or alternatively, to perturb the guided optical energy in the fiber core.
For example, when two fiber cores are closely spaced from each other by a spacing on the order of one wavelength or less, optical coupling occurs between the two fiber cores through the overlap of the evanescent fields of the two fiber cores. This structure can be used to construct optical fiber couplers.
One embodiment of the fiber devices of the present disclosure includes a substrate that is formed with an elongated groove on one substrate surface, and two openings respectively at two ends of the groove formed through the substrate to extend between the two sides of the substrate. An optical fiber is engaged to the substrate by passing through the two openings. The fiber has at least first, second, and third contiguous fiber portions, where the second fiber portion is disposed in the elongated groove on one side of the substrate, and the first and third fiber portions are located on or over the opposite substrate surface. The fiber cladding in the second fiber portion may be at least partially removed to form an optical coupling port for the fiber.
According to another embodiment, a fiber device may be formed in a substrate that includes grooves formed on both opposing sides of the substrate. The substrate has first and second opposing substrate surfaces, and first, second, and third openings that are spaced along a straight line and go through the substrate to extend between the first and the second substrate surfaces.
The first groove, elongated along the straight line and formed over the first substrate surface between the first and second openings, is configured to have a first end connected to the first opening and a second end connected to the second opening. The second groove, elongated along the straight line and formed over the second substrate surface between the second and third openings, is configured to have a first end connected to the second opening and a second end connected to the third opening. An optical fiber is engaged to the substrate by passing through the first, second, and third openings in the substrate to have a first fiber portion positioned in the first groove and a second fiber portion positioned in the second groove.